Wisconsin Energy announced Monday it has filed paperwork to acquire Integrys Energy Group for $9.1 billion in cash, stock and assumed debt.

The combined company, which will be called WEC Energy Group, would be the largest electric and gas utility in the Midwest.

WEC Energy Group would have corporate headquarters in Milwaukee, and have operating headquarters in Green Bay, Milwaukee and Chicago.

WEC Energy Group also owns 60 percent of American Transmission Company, a supplier of utility lines.

"We believe this combination provides a unique opportunity to create the premier regulated utility system in the Midwest, with superior service and competitive pricing for years to come," said Gale Klappa, chairman and CEO of Wisconsin Energy.

Following the sale, Klappa will become chairman and CEO of WEC Energy Group. Integrys CEO Charlie Schrock will remain in his role until the transaction is completed. He then plans on retiring.

The terms of the transaction have been approved by the boards of directors for both companies, and is subject to approvals from shareholders as well as several federal agencies.

Both companies anticipate the deal to be completed in the summer of 2015.